Make sure that your HP printer is set as the default printer on this particular computer from where you are doing the post & print because when you do a post & print NAV looks for the default printer unless you have specified a particular report to print to a different print via Printer selection table. In this case since its a post & print this printer should be installed on the machine you are printing and also should be set as the default printer.

What this will do is after posting the Cash receipt journal it will bring up the request page. In there you will click on Print and when you do that it will show you the printer name. This will tell you which printer its trying to use and based on that you can resolve this issue.